Structures for a field-effect transistor and methods of forming structures for a field-effect transistor. A semiconductor fin having a channel region, a nanowire arranged over the channel region of the semiconductor fin, a source/drain region connected with the channel region of the semiconductor fin and the nanowire, and a gate structure that overlaps with the channel region of the semiconductor fin and the nanowire. The nanowire has a first gate length, and the channel region of the semiconductor fin has a second gate length that is greater than the first gate length.